Railway signaling and frequency selective device for use in connection therewith



I. S. HOLLIDAY.

RAILWAY SIGNALING AND FREQUENCY SELECTIVE DEVICE FOR USE IN CONNECTION THEREWITH.

I I APPLICATION FILED JULY I2, ISIS.

Patented Dec. 21, 1920.

3 SHEETS-SHEET I.

J. S. HOLLIDAY. v RAILWAY SIGNALING AND FREQUENCY SELECTIVE DEVICE FOR UCE IN CONNECTION THEREWITH.

' APPLICATION FILED .IULY I2, 1916.

1,362,624, Patented Dec. 21, 1920.

3 SHEETS-SHEET 2- FIG-4 1. s. IHOLLIDAY.

RAILWAY S IGNALING AND FREQUENCY SELECTIVE DEVICE FOR USE IN CONNECTION THEREWITH.

- APPLICATION FILED JULY 12, 1915.

1,362 624, Patented Dec. 21, 1920.

3 SHEETS-SHEET 3.

FIG. 5 FIG-.SA

WITNESSES INVENTO Q W JJ C UNITED STATES PATENT OFFICE.

.ioiI'N s. HOLLIDAY, or w-ILKINsBURG, PENNSYLVANIA, ASSIGNOR TO THE UNIO SWITCH ,& SIGNAL COMP NY. or swIssvALn, PENNSYLVANIA, A CORPORATION.

OF PENNSYLVANIA.

RAILWAY SIGNALING AND FREQUENCY SELECTIVE DEVICE FOR USE IN CONNECTION THEREWITI-I.

Specification of Letters Patent.

Patented Dec. 21, 1920.

Application filed July 12, 1916. Serial No. 108.770.

To all whom it may concern.

Be it known that 1, JOHN S. Ho L DAY, a citizen of the United States, residing at \Vilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented certain new and useful Improvements 1n Railway Signaling and Frequenc Selective Devices for Use in Connection herewlth, of which the following is a specification.

My invention, relates to railway signaling, alternating currents for use in connection therewith.

One object ofmy invention to provide apparatus, which, when suppl ed with two alternating currents Cllfi ellng. in frequency, will produce a difference of potential across its terminals for one of said currents but not for the other, so that current responsive devices connected across said terminalswill receive said one current but not the other. Other objects of my invention w1ll appear in the following description.

I shall describe a few forms and arrangements of apparatus embodying my invention and then point out the novel features thereof in claims.

In the accompanying drawings, Figure 1 is a diagrammatic view showing a railway signaling system comprising one form of frequency selective device embodying my invention. Fig. 2 is a diagrammatic view showing separately the frequency select ve device shown in Fig. 1, this device being inverted for convenience in reading in connection with the vector diagram pertaining thereto shown in Fig. 2*. Fig. 2 is a vector diagram showing the theoretical voltages in the various members and across the terminals of the form of device shown In Figs. 1 and 2. Fig. 3 is a group of curves showing results'obtained by an experimental test of the form of device shown in Figs. 1 and 2. Figs. 4, 5, 6 and 7 are diagrammatic views showing modified forms of frequency selective devices embodying my invention. Figs. 4 5 6 and 7 are vector diagrams showing the theoretical voltages in the various members of the devices shown in Figs. 4, 5, 6 and 7 respectively.

Similar reference characters refer to similar parts in each of the views.

Referring first to Fig. 1, reference charand to frequency selective devices for Y acters 4 and 5 designate the track rails of an electric railway, which rails are divided into sections by insulated joints 2. In the drawing I have shown only one section A-B and the beginning and end respectively of the two adjoining sections. For the control of trailic through section A-B I provide a signal S having a semaphore arm 20, which, when in the vertical position as shown, indicates proceed, and which, when in the horizontal position, indicates stop. These positions of the signal arm are controlled by a relay R, through the following circuit: from a battery E, through contact 6 of relay R, wire 8, operating mechanism of si nal S (not shown) and wire 7 ,to battery The signal S, therefore, indicates proceed or stop, according as relay R is'energized or deenerqized.

Relay it is controlled by a track circuit for section A-B, which circuit comprises the track rails 4 and 5 of the section, a source of signaling current connected to these rails adjacent one end of section A--B and a current responsive device connected to theserails near the other end of section A-B. As here shown, the source of signaling current for the track circuit is a transformer M,-the primary of which receives signaling current from an alternator H through a transmission line N, and the secondary of which is connected to the track rails 4 and 5 by wires 10 and 13 respectively. The current responsive device, as here shown, is a transformer F, the primary of which receives the signaling current from the track rails through wires 11 and 12, and

the secondary of which delivers this current to relay R as I shall presently describe.

The relay R is connected to the secondary of transformer F by a frequency selective device comprising in this form of my inven tion, inductances 21 and 22, a resistance 23 and a condenser 24 (see alsoFig. 2). Inductance 21 and condenser 24 are connected to the extremities a and 0 respectively of the secondary coil of transformer F, and resistance 23 and inductance 22 are connected to an intermediate point Z) of this coil. Inductance 21 and resistance 23 are joined at a terminal 03 and inductance 22 and condenser 24 are joined at a terminal f. The relay R is connected to terminals 11 and f as shown in Fig. 1, and the voltage across terminals d and f is the voltage applied to the relay winding.

Referring now to the vector diagram Fig. 2 vectors a b and b 0' represent respectively the voltages in the sections a b and b c of the secondary coil of transformer F. The voltages across inductance 21 and resistance 23 (at the frequency of the signaling current, which frequency I assume to be cycles for reasons pointed out hereinafter) are indicated respectively by vectors a d and b d and the voltages across inductance 22 and condenser 24 are represented by vectors b f and c f. The open circuit difference in potential between terminals d and f is represented by a vector d f connecting the points 03 and f on the vector diagram. Thus it appears that the track circuit voltage on transformer F causes a flow of signaling current in the winding of relay R, which currentholds contact 6 of the relay closed so that signal S is caused to indicate proceed.

When a vehicle V acce ts this signal and enters track section A- the wheels and axles thereof form a low resistance shunt from one rail of the section to the other. Transformer F, therefore, is short circuited at the track rails and receives but a negligibly small amount of signaling current, so that relay R is denergized and causes us it appears that relay R is responsive to the signaling current 1n transformer F and controls the signal S to indicate proceed or stop according to the absence or resence of vehicles in section A-B.

ropulsion current for the operation of the cars or trains along the railway is furnished by an alternator G, one terminal of which is connected to .a trolley wire or third rail L, and the other. terminal of which is grounded to the track rails. This propulsion current flows from one terminal of the generator through wire L, vehicle V, track rails 4 and 5 in parallel to the other terminal of the generator G. In flowing through the vehicle the current drives the propulsion motors which I have not shown on the drawing. As noted hereinbefore the track rails are divided into sections by insulated joints 2. To pass the propulsion current around these joints, without interfering with the track circuits hereinbefore described, I provide impedance bonds for the joints, each bond comprising iron core impedance coils 3 and 3 connected between the track rails, one on each side of the joints. The middle points of these coils are connected together by a conductor 3 At each bond the propulsion current enters both ends of the coil 3 simultaneously from both track 'rails and flows to the middle point of the coil in opposite directions.

si nal S to assume the stop indication.- T

From there it flows through conductor 3 to the middle point of coil 3. Here the current divides, one half flowing through one part ofcoil 3 to the track rail 4 of the next section,- and the other flowing through the other part of coil 3 in the opposite direction to the track rail 5 of that section. The propulsion current, therefore, traverses the two halves of each of the coils 3 and 3 in opposite directions so that the resultant magnetic flux in the cores of these coils is practically zero. Consequently, the impedence of these coils to the propulsion current is reduced practically to the ohmic resistance of the coil windings, which can be made very low. These impedance bonds, however, prevent the flow of signaling current from one rail to the other of a section, because this current magnetizes the cores of these coils and is therefore met by a high impedance which reduces this flow of the signaling current to a small amount. Thus it is apparent that the impedance bonds offer but a small resistance to the proper flow of the propulsion current, while at the same time they prevent an improper flow of the signaling current.

For a variety of causes, such for example as unequal bonding of the track rails, it

may happen that for the propulsion current the voltage of one track rail in section A-B is higher than the voltage of the other rail, so that a part of the propulsion current flows from one track rail to the other, through transformer F, and therefore also through the impedance device connected to this transformer. It should here be noted that the propulsion current differs in frequency from the signalin current which normally energizes trans ormer F. For purposes of illustration, and to correspond with present day commercial practice, I shall assume herein that the frequency of the propulsion current is 25 cycles, whereas the frequency of the signaling current is 60 cycles, but it is understood that I do not wish to be limited thereto, my invention being applicable to currents of any desired frequencies.

As is well known, the reactance of an inductance or a condenser to any current depends upon the frequency of that current. If, therefore, the voltage of the propulsion current across the terminals of the secondary of transformer F is represented by vector a c, the vectors representing the voltage drops of the propulsion current through the impedance devices-21, 22, 23 and 24 will not be the same as the vectors, hereinbefore described, representing similar voltages for the signaling current. The propulsion current voltages consumed in inductance 21 tance 22 and condenser 24 are shown respectively by vectors 6 f" and c f". Points (2" and f" on the vector diagram coincide, showing that for the propulsion current the voltage of terminal 03 is the same as the voltage of terminal It appears, therefore, that the propulsion current, even when it energizes transformer F, cannot affect relay R in its control of signal S.

' The correct proportioning of the impedance devices and the proper location of point 6 on transformer F may be determined either by experimental trials or by theoretical calculations. It should here be noted that the points d and d are located, theoreticle a: of which vector (1 b is a chord. Similarly, points f and f are located on the circumference of a circle of which vector 7) c is a chord. The point of intersection of these circles (other than 1)) is the point on the vector diagram at which both points (1 and f" must be located in order that the potentials at terminals d and f of the impedance devices may be equal.

The curves in Fig. 3 (obtained by experiment) show the voltages across the relay terminals d and f for various 60 and 25 cycle voltages on the terminals 0; and 0 of transformer F. It is evident that the 60 cycle voltage at the relay is comparatively high and approximately proportional to the 60 cycle voltage at the transformer'F, whereas the 25 cycle voltage at the relay remains practically zero for all values of 25 cycle voltage applied at this transformer.

In Fig. 4 I have shown a modification of the impedance devices connected between transformer F and terminals d and f. In this modification a resistance 25 is connected from extremity a of the secondary coil of transformer F to terminal d and a condenser 26 is connected from this terminal to a point 12,, of intermediate potential on coil ac. Similarly, an inductance 27 is connected from a second intermediate tap b, of coil ac to terminal 7 and a condenser 28 is connected between this terminal and the extremity a of coil ac. Vector diagram 4 shows the vector relations for a proper adjustment I of the impedance devices and correct locations of points 6 and 6 If vector at 0' is chosen to represent the voltage on the secondary (10 of transformer F, vector a d represents to scale the voltage for 60 cycle current consumed in resistance 25, and vector d 7), represents the voltage at 60 cycles across condenser 26. Similarly, the 60 cycle voltage across inductance 27 is shown by vector 12, f and the voltage at this frequency across condenser 28 is shown by vector a f. The 60 cycle voltage between terminals d and f, which voltage is applied to the relay terminals, is represented therefore by vector d f. However, when there is a 25 cycle voltage a c on the secondary coil as of the transformer F, the voltages for this frequency across resistance 25 and condenser 26 are shown by vectors a d and b, (1 respectively, and the voltages in impedance 27 and condenser 28 are represented by vectors 7/ f" and c 7, respectively. Points d and f" coincide, hence the potentials of terminals d and f are equal for 25cycle current, so that this current cannot energize the relay connected across the terminals. In the theoretical vector diagram points a, 5' (1 and d are again located on the circumference of circle X and points 6' 0, f and 7'" are located on the circumference of circally at least, on the circumference of a c1rcle 3 Points d and f" are superimposed at the point of tangency of these circles.

Still other modifications of the impedance devices connected between the secondary coil of transformer F and the terminals 0? and f are shown in Figs. 5, 6 and 7, and their corresponding theoretical vector diagrams in Figs. 5 6 and 7 respectively. In view of the foregoing description, these figures are easily understood and do not require further explanation.

It should here be noted that although I have shown in each of the drawings the impedance devices connected to the secondary coil of a transformer F, the use of such a transformer although often preferable, is not necessary. In fact an impedance coil or any other device which can be tapped at a point or points of potential intermediate the potentials of the extremities of the device may be substituted for the transformer, as is readily understood by those versed in the art.

Although I have illustrated my invention as applied to a track circuit for railway signaling, it is understood that it is applicable in many instances, wherever it is desired to select between alternating currents differing in frequency.

Although I have herein shown and described only a few forms ofapparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. A frequency-selective device comprising a current-carrying, device in which alternating current differing in frequency may flow at times, two current-delivery terminals, and a combination of impedance devices connected between said current-carrying device and said terminals and arranged to react differently to currents of different frequencies so that both terminals are at substantially. the same voltage for current of a pre-determined frequency but not for currents of other frequencies.

2. A frequency-selective device comprising a current-carrying device in which alternating currents differing in frequency may flow at times, two current-delivery terminals, impedance devices connected from a plurality of points differing in potential on in frequency may flow at times, a shunt I comprising series-connected impedance devices connected across one portion of said device, a second shunt comprising seriesconnected impedance devices connected across another portion of said device, said shunts reacting differently to currents of different frequencies so that for current of a pie-determined frequency ,a point on one shunt is always at substantially the same potential as a point on the other shunt.

4;. In combination, a current-carrying device in which alternating currents differing in frequency may flow at times, two currentdelivery terminals, and a pair of impedance devices connected from said device to each of said terminals, said pairs of devices being arranged to react differently to currents of different frequencies and in such manner that said terminals are always at substantially equal potential for current of one frequency flowing through the device but not for current of another frequency.

5. In combination, a current-carrying device in which alternating currents differing in frequency may flow at times, two impedance devices joined in series and connected across one portion of said current-carrying device, and two other impedance devices joined in series and connected across another portion of said current-carrying device, said impedance devices being so proportioned and the points at which they are connected to the current-carrying device being so chosen that for current of a redetermined frequency the two junction points of the im-' pedance devices are at equal potential.

6. In combination, a current-carrying device in which a plurality of alternating 'ing device to an intermediate point thereon,

said impedance devices being so proportioned and said points at which said impedance devices are connected to said currentcarrying device being so chosen, that for current of a predetermined frequency the two junction points of the impedance devices are always at equal potential.

7. In combination, a current-carrying device in which a plurality of alternating currents differing in frequency flow at times, an inductance and a resistance connected in series from an outside point on said currentcarrying device to an intermediate point thereon, an inductance and a condenser connected in series from an intermediate point on said current-carrying device to the other outside point thereon, said inductances, resistance and condenser being relatively so proportioned and the points at which they are connected to the current-carrying device being so chosen that for currentof a pr determined frequency the junction point of the inductance and resistance is always at substantially the same potential as the junction point of the inductance and condenser.

In testimony whereof I affix my signature in presence of two witnesses.

JOHN S. HOLLIDAY.

W'itnesses:

A. HERMAN WEGNER, GEO. A. WASHBURN. 

